Operation of a typical breakout machine involves positioning the work piece in the headstock and closing the clamp cylinder onto the work piece, which anchors the work piece to the bed, then positioning the tailstock at the appropriate position and closing the clamping cylinders. The generated force is applied through the fixed moment arm, which applies that generated torque to the work piece. The magnitude of the torque is variable, by adjusting the pressure that is applied to the torque cylinders.
Breakout machines currently use hydraulic pressure supplied to the torque cylinders to determine the magnitude of the torque being applied to the work piece. The hydraulic pressure supplied to the torque cylinders is varied to adjust the torque output. The torque cylinder piston area (break side) and the piston area minus the rod area (make side) are set, as well as the moment arm length or the torque cylinders. At a given pressure, the force generated multiplied by the torque arm length is used to determine the magnitude of the torque applied by one of the torque cylinders and then multiplied by two. Two torque cylinders applying torque in unison is the preferred method, as it reduces the amount of error. There are errors caused by the hydraulic system, mechanical system, as well as the geometry of the machine that limit its accuracy and performance.
Hydraulic system errors are the total sum of all the small losses due to flow through the hydraulic components and force lost to friction operating components. Pressure and flow moves pistons or valve spools and have spring forces to work against. Each hydraulic component has a number of seals or wear rings that cause pressure losses. The clamp cylinders along with the torque cylinders are relatively large cylinders that all have large stiff seals and large wear rings. These components can be designed to minimize these losses, but the combination of these components can cause significant total loss. The system pressure applied to the torque cylinders must be accurate when varied from 0 through 3,000 psi. An error of 100 psi is not significant at the maximum system pressure of 3,000 psi, but such an error is significant to the accuracy of the lower range of torque application. The hydraulic error outlined is one of the errors that limits the accuracy of the torque that can be applied at the low end of its range. Generally, existing machines offer a minimum torque application of 4,000 lb-ft to 5,000 lb-ft is specified for the “make up” range. Current drilling industry practice is to use smaller diameter tools with smaller diameter threaded connections, which call for lower make up torques being applied. This limits the applications of current breakout machines.
Mechanical errors are caused by the bearings, hinges, pivot points, and hoses all causing friction during operation. Good design practice reduces the friction these items cause. A good maintenance/lubrication program will minimize the friction and wear caused, but will not eliminate it. As the machine is operated friction and wear will occur.
The arrangement of the torque cylinders causes an error due to the arc the cylinders travel through a make/break cycle. The moment arm length changing through the torque cylinder travel causes this error, the moment arm length is used to determine the magnitude of the torque being applied. Breakout machines that use the system pressure to determine the torque being applied must have a set moment arm length. Using a moment arm length in one position or an average moment arm length all add an error due to the geometry. Again, good design practice can be used to minimize this error. One method is to limit the arc length the torque cylinders travel. Smaller arc travel results in less moment arm length change, but require more arc travel cycles to complete one full revolution of the work piece.
The errors combine to create a total amount of error affecting the accuracy of the torque being applied. The effects of wear and tear on a machine and its systems results in a breakout machine that requires re-certification on a annual or bi-annual basis to maintain accurate torque application. The re-certification process is at the end users expense and can be very expensive. The result of the re-certification process, is a chart that indicates the actual torque being applied for a given torque setting read on the breakout machine. This can be very confusing to the operator who has go back and forth between the chart and the machine to determine the torque output, increasing the possibility of operator error.